The objective of this project is to test and refine a system for the early identification of mass lesions (delayed intracranial hematomas, brain edema), prior to the development of the herniation syndrome and irreversible brain damage. Intracranial pressure (ICP) does not begin to change until the buffering capacity of the craniospinal axis has been virtually exhausted. At this point, an exponential increase in ICP may result from even a small increase in the size of the mass lesion. Currently available measures of intracranial compliance such as the pressure volume index (PVI), have not found widespread use because their intermittent nature, invasiveness and practical constraints. It has been shown that the vibrational characteristics of the brain, as determined by analysis of the ICP waveform, can provide reliable and useful data relating to intracranial compliance. Specifically, shifts in the power weighted mean frequency in the range of 4-15 Hz, as measured by discrete Fourier transform analysis, correlate well with changes in the brain's compliance as measured by the PVI. The mean of these high frequency components, referred to as the high frequency centroid (HFC), correlates inversely with the PVI. In other words, the stiffer the brain, the higher the frequency of vibration associated with each arterial pulsation. Based on this observation, a monitoring system has been developed which can provide continuous on-line data on the state of intracranial compliance. Preliminary studies have shown this system to be safe and reliable. This project is a prospective evaluation of the high frequency centroid monitor in comatose head injury patients. Each episode of an increase in the numeric value of the HFC, detected by continuous monitoring, will be confirmed by measurement of the PVI. If reduced intracranial compliance is confirming (PVI<13), a CT scan will be obtained to determine the cause. If a mass lesion is detected, the appropriate surgical intervention will be undertaken. It is expected that with the use of the HFC monitor, the development of an intracranial mass lesion(hematoma, edema) will be identified and treated earlier than is currently possible with conventional ICP monitoring, hourly neurological exams and even 8 hourly PVI determinations. This can potentially prevent, or limit, brain damage secondary to compression, and possibly enhance ultimate neurological recovery.